The present invention is related to the field of navigational systems and devices and, more particularly, to satellite-based navigational systems and devices capable of detecting inclination and changes in inclination of an object in motion.
In many areas, on-board, satellite-based, three-dimensional travel navigation systems using, for example, the global positioning system (“GPS”) have improved dramatically over the past few years. However, such navigation systems continue to have limited resolution, which displays erroneous data to the vehicle operator or passenger/navigator. Indeed, although satellite receivers are adapted to provide vertical resolution that is suitable for displaying the location of the vehicle, poor resolution manifests and is further complicated at, for example, complex interchanges having plural overpasses, underpasses, on-ramps, and off-ramps that overlie or underlie each other.
When elevated roadways and viaducts follow the same or substantially the same route of an underlying roadway, it is difficult for the navigational system to differentiate between the two roadways and, moreover, on which of the roadways the vehicle is actually traveling.
A device using an altimeter is shown in FIG. 2. The device 20 includes a magnetic compass 21, a pressure sensor 23, and a control unit 22. The pressure sensor 23 is adapted to provide pressure measurements from which an altitude can be determined. In theory, the altimeter device 23 would be able to measure the difference in altitude between the elevated roadway or viaduct and the underlying roadway. In practice, however, the vehicle must travel a sufficient horizontal distance (minimum travel distance) on the underlying roadway or on the elevated roadway in order to receive sufficient altitude data to make a determination as to on which roadway the vehicle is traveling. Thus, in many cases having short horizontal distances, the navigational system has no way of correctly assessing the vehicle's true position.
A device using an accelerometer is shown in FIG. 3. The device 30 includes a magnetic compass 31, a two-axis accelerometer 33, and a control unit 32. The accelerometer 33 can be used like an inclinometer, to measure the pitch of the vehicle and further, with data from the magnetic compass 31, to measure variations in the pitch angle.
Pitch is defined as an angle between an object's longitudinal axis and a local horizontal plane. By convention, in aerospace applications, positive pitch refers to “nose up” and negative pitch refers to “nose down”. Each of these solutions, however, requires additional circuitry, e.g., the addition of an accelerometer and/or of a gyroscope, which creates additional cost and adds to the sophistication of manufacture. Furthermore, the added circuitry increases the size and power needs of the receiver system to which they are added.
Disadvantageously, with accelerometers, it is difficult to differentiate between acceleration data resulting from natural changes in speed of the vehicle (acceleration, deceleration) and data resulting from a slope. Therefore, it would be desirable to provide a simple and economical navigational system and/or navigational device that can quickly and accurately measure and/or detect whether or not a moving vehicle is operating on a sloped roadway or not. Moreover, it would be desirable to provide a navigation system and/or navigation device that does not require additional embedded circuits and that is not influenced by speed variations.